This invention relates to tire and wheel assemblies for vehicles and more particularly to pneumatic tire and wheel assemblies having run flat capabilities.
Pneumatic vehicle tires in conventional use offer good riding characteristics and are light in weight but suffer the drawback of becoming inoperative as a practical matter upon loss of air. Such loss of operability is not only undesirable from the safety standpoint, but also requires that an additional tire be carried by the vehicle as a precaution against the loss of air from an operating tire. The additional tire however adds weight and takes up available space and is therefore highly undesirable particularly to present day automobile manufacturers who are seeking to reduce size and weight of automobiles in order to meet more stringent government fuel economy requirements for their vehicles as well as safety requirements.
An ideal solution to the problem of inoperativeness upon loss of air from pneumatic tires is to impart a "run flat" capability to the tire which would permit the tire to continue to be operative for at least a reasonable period of time following deflation. A popular approach to imparting a run flat capability to pneumatic tires is to provide some sort of inner annular member within the tire having sufficient resiliency to prevent complete collapse of the tire tread wall upon deflation. Thus for example metallic or other rigid material annular extensions to the tire rim have been suggested which extend into the air chamber of the tire a distance but stop short of the tire tread wall in order to preserve the good ride of the pneumatic tire. The metal extensions typically act to support the tread wall and sometimes also to hold the tire beads in place upon deflation of the tire. Metal extensions however add considerable weight to the wheel assembly and offer poor riding characteristics in the run flat condition due to the rigidity of the extension itself. Also, special rim designs are usually required with such extensions such as for example is shown in U.S. Pat. No. 2,844,180 to Omeron. More recent advancements in this area are shown for example in U.S. Pat. Nos. 3,942,571 to Kraft and 3,990,491 to Hampshire and Watts, where the metallic extension is C-shaped in cross section to lessen its rigidity and is further shaped such that it can be used with the conventional one piece drop-center tire rim. Inner annular members of less rigid material than metal such as for example foamed polymer inserts have also been suggested in the art. Such inserts might improve run flat riding characteristics but generally they suffer from lack of adequate dimensional stability and high heat build-up which are especially important considerations when the tire is to be driven in a run flat condition a lengthy distance and/or at the relatively high rates of speed required in modern highway driving. Also, due to the high volume occupied by typical foam polymer inserts, use of such materials with conventional one piece rims is limited since sufficient space must be left within the tire cavity to permit mounting of the tire. One example of a foamed polymeric insert said to be mountable upon a conventional one piece tire rim is shown in U.S. Pat. No. 3,814,158 to Ryder. The foamed polyurethane insert shown in this patent has a pair of annularly extending bead wires to add structural stability and support and further has a central annular space to permit collapse of the insert during mounting of the tire upon a conventional one piece drop center rim. More recently published patents in the area of run-flat inserts for pneumatic tires include U.S. Pat. No. 4,121,640 to Henning et al and U.S. Pat. No. 4,137,894 to Gardner et al, which make use of an insert comprised generally of an inner pneumatic member of smaller diameter than the tire which supports the tire carcass when the tire is operating in the run-flat condition.